1. Field of the Invention
The present invention relates to a road shape estimation apparatus to eliminate improper nodes for calculating a radius of curvature for a curve and to a curve approach speed control apparatus using the road shape estimation apparatus.
2. Description of the Related Art
JP-A-4-236699 proposes a vehicle traveling system which calculates an allowable approach speed for a curve in front by using data (node data) on points in ground (nodes) shown on a road map of a navigation device, detects a speed higher than the allowable approach speed, i.e., an overspeed state for the curve in front, and issues an alarm or perform a speed reduction control.
The applicant of this invention has proposed in JP-A-11-2528 a method for determining a radius of curvature for a curve based on a plurality of node data output from the navigation device.
That is, for three consecutive nodes, the center node and the two other nodes on both sides are connected with straight lines, and the lengths of the two straight lines are compared. A half the length of the shorter straight line is taken from the center node on both straight lines to find mid points. At the mid points normal lines perpendicular to their own straight lines are drawn until they intersect each other. The distance from the point of intersection to each mid point is set as a radius of curvature for a curve.
A method in JP-A-11-83501 calculates, based on a radius of curvature for a curve and a lateral acceleration, an allowable curve approach speed at which the vehicle can safely negotiate the curve in front, compares the allowable curve approach speed with the car speed in a predetermined procedure to check whether the curve can be safely negotiated, and, if the decision indicates an overspeed, issues an alarm prompting the user to decrease the speed or forcibly performs a speed reduction control as required.
When calculating the curve""s radius of curvature based on the distances between the three consecutive nodes, if the node distances are extremely short, the curve""s radius of curvature based on half the node distance is likely to be calculated far smaller than the actual curve""s radius of curvature. As a result, if the allowable curve approach speed is calculated based on the erroneously calculated curve""s radius of curvature, it will be set to an extremely slow speed, giving rise to a problem that even when the car is actually traveling at a speed at which it can safely negotiate the curve, an alarm may be issued or the speed reduction control activated, making the driver feel incongruous.
The present invention has been accomplished under these circumstances to provide a road shape estimation apparatus and a curve approach speed control apparatus using the road shape estimation apparatus, which, even when the node intervals are extremely short, can calculate a curve""s radius of curvature approximating the actual curve, set an appropriate allowable curve approach speed and thereby alleviate a sense of incongruity from the driver.
To achieve the above objective, a first road shape estimation apparatus according to the present invention comprises inputting a plurality of node data concerning a road in front from a navigation device, calculating, based on the node data, a node interval between each node and an adjacent node and a node angle for each node, and, based on the node intervals and the node angles, calculating a curve""s radius of curvature for each node, wherein the road shape estimation apparatus detects, based on the node intervals and the node angles, a node which constitutes a curve""s radius of curvature calculation removal point, and calculates the curve""s radius of curvature by removing the node which constitutes the curve""s radius of curvature calculation removal point.
In this configuration, when inputting a plurality of node data concerning a road in front from a navigation device, calculating, based on the node data, a node interval between each node and an adjacent node and a node angle for each node, and, based on the node intervals and the node angles, calculating a curve""s radius of curvature for each node, the apparatus detects, based on the node intervals and the node angles, a node which constitutes a curve""s radius of curvature calculation removal point, and calculates the curve""s radius of curvature by removing the node which constitutes the curve""s radius of curvature calculation removal point.
A second road shape estimation apparatus is characterized in that, in the first road shape estimation apparatus, when the node interval is equal to or less than a preset node interval, at least one of nodes at both ends of the node interval is taken as the curve""s radius of curvature calculation removal point.
With this configuration, when the node interval is equal to or less than a preset node interval, at least one of nodes at both ends of the node interval is taken as the curve""s radius of curvature calculation removal point.
A third road shape estimation apparatus is characterized in that, in the first road shape estimation apparatus, when the node interval is equal to or less than a preset node interval and bending directions of the node angles calculated at the two nodes situated at the both ends of the node interval are opposite, at least one of the two nodes is taken as the curve""s radius of curvature calculation removal point.
With this configuration, when the node interval is equal to or less than a preset node interval and bending directions of the node angles calculated at the two nodes situated at the both ends of the node interval are opposite, at least one of the two nodes is taken as the curve""s radius of curvature calculation removal point.
A fourth road shape estimation apparatus is characterized in that, in the first road shape estimation apparatus, when the node interval is equal to or less than a preset node interval and a larger one of the node angles calculated at the two nodes situated at the both ends of the node interval is equal to or more than a preset maximum threshold angle, at least one of the two nodes is taken as the curve""s radius of curvature calculation removal point.
With this configuration, when the node interval is equal to or less than a preset node interval and a larger one of the node angles calculated at the two nodes situated at the both ends of the node interval is equal to or more than a preset maximum threshold angle, at least one of the two nodes is taken as the curve""s radius of curvature calculation removal point.
A fifth road shape estimation apparatus is characterized in that, in the first road shape estimation apparatus, when the node interval is equal to or less than a preset node interval and a smaller one of the node angles calculated at the two nodes situated at the both ends of the node interval is equal to or less than a preset minimum threshold angle, at least one of the two nodes is taken as the curve""s radius of curvature calculation removal point.
With this configuration, when the node interval is equal to or less than a preset node interval and a smaller one of the node angles calculated at the two nodes situated at the both ends of the node interval is equal to or less than a preset minimum threshold angle, at least one of the two nodes is taken as the curve""s radius of curvature calculation removal point.
A sixth road shape estimation apparatus is characterized in that, in the first road shape estimation apparatus, when an angle formed by a line connecting first two of four consecutive nodes and a line connecting last two nodes is equal to or less than a preset minimum threshold angle and a node interval connecting two middle nodes is equal to or less than a preset node interval, at least one of the two middle nodes is taken as the curve""s radius of curvature calculation removal point.
With this configuration, when an angle formed by a line connecting first two of four consecutive nodes and a line connecting last two nodes is equal to or less than a preset minimum threshold angle and a node interval connecting two middle nodes is equal to or less than a preset node interval, at least one of the two middle nodes is taken as the curve""s radius of curvature calculation removal point.
A seventh road shape estimation apparatus is characterized in that, in the second road shape estimation apparatus, the preset node interval is set by multiplying a preset node interval calculation coefficient by a road width coefficient.
With this configuration, the preset node interval is set by multiplying a preset node interval calculation coefficient by a road width coefficient.
A eighth road shape estimation apparatus is characterized in that, in the seventh road shape estimation apparatus, the preset node interval calculation coefficient is set for each road kind.
With this configuration, the preset node interval calculation coefficient is set for each road kind.
A ninth road shape estimation apparatus is characterized in that, in the fourth road shape estimation apparatus, the maximum threshold angle or the minimum threshold angle is set by multiplying a preset reference angle by a ratio between the node interval and the preset node interval.
With this configuration, the maximum threshold angle or the minimum threshold angle is set by multiplying a preset reference angle by a ratio between the node interval and the preset node interval.
A first curve approach control apparatus using any one of the first to ninth road shape estimation apparatus is characterized in that when a node interval between two nodes adjacent to, and on both sides of, the node which is taken as the curve""s radius of curvature calculation removal point is equal to or less than a preset node interval, an alarm or deceleration control for at least one of the two nodes is prohibited.
With this configuration, when a node interval between two nodes adjacent to, and on both sides of, the node which is taken as the curve""s radius of curvature calculation removal point is equal to or less than a preset node interval, an alarm or deceleration control for at least one of the two nodes is prohibited.
A second curve approach control apparatus using any one of the first to ninth road shape estimation apparatus is characterized in that when a curve angle of at least one of two nodes adjacent to, and on both sides of, the node which is taken as the curve""s radius of curvature calculation removal point is equal to or less than the preset minimum threshold angle, an alarm or deceleration control for the at least one node is prohibited.
With this configuration, when a curve angle of at least one of two nodes adjacent to, and on both sides of, the node which is taken as the curve""s radius of curvature calculation removal point is equal to or less than the preset minimum threshold angle, an alarm or deceleration control for the at least one node is prohibited.